Sintered ferrite body, chip inductor, and composite LC part

ABSTRACT

A ferrite composition comprising ferrite, borosilicate glass, and optionally boron oxide can be fired at a relatively low temperature of up to 950° C. into a sintered body having improved mechanical strength and electromagnetic properties. The sintered ferrite body is used to form a chip inductor. The inductor is combined with a capacitor to form a composite LC part.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a sintered ferrite body useful as variousmagnetic materials, a chip inductor using the sintered body as amagnetic material, and a composite LC part having capacitor and inductorsections in a common chip.

2. Prior Art

A variety of ferrites have been used as various magnetic cores becauseof their magnetic properties. Among others, nickel base ferritesincluding Ni ferrites, Ni-Zn ferrites, and Ni-Cu-Zn ferrites have beenwidely used as low-temperature sinterable material to which printing andgreen sheet techniques are applicable.

Sintered ferrite bodies, however, have unsatisfactory mechanicalstrength. The sintering temperature must be raised to increase thedensity of a sintered body before the mechanical strength can beenhanced. This undesirably invites an increase of manufacturing expense.

Japanese Patent Application Kokai Nos. 58-135133, 58-135606, 58-135607,58-135608 and 58-135609 disclose to add glass to ferrite to reduceshrinkage upon sintering, but the specific composition of glass is notdisclosed therein. These sintered bodies are insufficient in denisty,mechanical strength, and high-frequency properties. These drawbacks areassumed to be caused by non-use of the borosilicate glass which is usedin the present invention as described later.

Japanese Patent Application Kokai No. 51-151331 and U.S. Pat. No.4,540,500 disclose ferrite having up to 5% by weight of lithiumborosilicate glass added thereto. The excellent effects of the presentinvention will not be attained in the ferrite body because of a lessamount of glass.

Japanese Patent Application Kokai No. 59-90915 discloses to form a glassintermediate layer between a conductive layer and an insulating layer.Such a construction will cause Q value drop and insufficient control ofcoefficient of linear expansion in forming a chip inductor.

Chip inductors and composite LC parts having inductor and capacitorsections in a common chip are known as typical parts in which ferritefinds application. Chip inductors are usually prepared by forming apaste of ferrite and applying the ferrite paste by printing or greensheet technique to form a laminate having an internal conductor embeddedtherein, followed by sintering. They also suffer from the problems thatmechanical strength is low and the sintering temperature must be raisedto increase mechanical strength.

These inductors have unsatisfactory frequency response of inductance andQ value. For example, their inductance and Q value approachsubstantially zero at a high frequency region in excess of 200 kHz.Frequency response may be improved by using a non-magnetic ceramic in aninductor section to form a coreless coil. The resulting inductor,however, has an insufficient inductance and Q value.

Composite LC parts having inductor and capacitor sections in a commonchip suffer from problems that separation or warpage occurs at the LCinterface during sintering because of the difference of shrinkagebetween the ferrite of the inductor section and the dielectric materialof the capacitor section and a crack occurs because of the difference ofcoefficient of linear expansion, failing to fulfil the function as asurface packaged part.

Sintered ferrite bodies find other applications as various magneticcores, magnetic shields, electromagnetic radiation shields, andattenuators. In these applications, it is also desired to improvesintering temperature, sintered density, and mechanical strength as wellas frequency response of electromagnetic properties such as magneticpermeability loss.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a ferrite compositionwhich can be fired at a lower temperature into a sintered body havinghigher mechanical strength and improved high frequency properties ascompared with conventional ones.

Another object of the present invention is to provide such a sinteredferrite body.

A further object of the present invention is to provide a chip inductorof a laminate structure having a ceramic magnetic layer of the sinteredferrite composition and an internal conductor layer.

A still further object of the present invention is to provide acomposite LC part having inductor and capacitor sections in a commonchip which undergoes neither separation or warpage at the LC interfaceduring simultaneous sintering.

According to a first aspect of the present invention, there is provideda sintered ferrite body comprising a ferrite and a borosilicate glass.The borosilicate glass comprises about 15 to about 75% by weight basedon the weight of the body. The ferrite body may further contain boronoxide.

According to a second aspect of the present invention, there is provideda chip inductor comprising at least one ceramic magnetic layer and atleast one internal conductor layer placed one on the other, the ceramicmagnetic layer containing a ferrite and a borosilicate glass, and theborosilicate glass comprises about 15 to about 75% by weight based onthe weight of the body. The ceramic magnetic layer may further containboron oxide.

According to a third aspect of the present invention, there is provideda ceramic composite LC part comprising a capacitor section including aceramic dielectric layer and an electrode layer placed one on the other,and an inductor section including a ferrite magnetic layer and aninternal conductor layer placed one on the other. The capacitor sectionis integrated with the inductor section. The ceramic magnetic layercontains a ferrite and a borosilicate glass, and the borosilicate glasscomprises about 15 to about 75% by weight based on the weight of theceramic magnetic layer, and a ceramic composite LC part may furthercontain boron oxide.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the presentinvention will be more readily understood from the following descriptionwhen taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a partially cut-away schematic illustration of a chip inductoraccording to one embodiment of the present invention; and

FIG. 2 is a partially cut-away perspective view of a composite LC partaccording to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a sintered ferrite body comprising aferrite and a borosilicate glass. The ferrite body may preferablycontain boron oxide. A composition of ferrite and borosilicate glass canbe sintered at relatively low temperatures of up to 950° C., especiallyup to 900° C. Even at such low temperatures, the composition can besintered to a sufficiently high density to provide mechanical strength.

The ferrite used herein encompasses all soft ferrites having well-knownspinel structure although ferrites containing at least one memberselected from Ni, Cu, Mn, Zn, and Fe are preferred. Nickel base ferritesare preferred because they are useful for high-frequency applicationsand can be sintered at relatively low temperatures. Included areNi-ferrite, Ni-Cu ferrite, Ni-Zn ferrite, Ni-Cu-Zn ferrite, and similarferrites having Li added thereto. In nickel base ferrites, the contentof Ni preferably ranges from about 45 to about 55 mol % calculated asNiO. Part of the nickel may be replaced by up to 40 mol % of Cu, Zn orLi or a mixture thereof. The nickel base ferrites may contain up toabout 5% by weight of Co or Mn, and further up to 1% by weight of Ca,Si, Bi, V or Pb or a mixture thereof.

The composition of the present invention is preferably obtained byblending ferrite with about 15 to 75% by weight, more preferably about25 to about 35% by weight of borosilicate glass. There is somepossibility that less than about 15% by weight of borosilicate glassadded is too small to be effective. More than about 75% by weight ofborosilicate glass means a too much content of glass ingredient. Such aglass rich composition tends to adhere to a support and largely changesits shape during firing, and has a high degree of deformation and a lowmagnetic permeability.

The borosilicate glass used herein includes ordinary borosilicate glass,alumina borosilicate glass, alkali borosilicate glass, and otherborosilicate glasses. With the use of borosilicate glass, the sinteredferrite body of the present invention has high mechanical strength, andimproved electromagnetic properties at high frequencies including a lowloss and a high Q value. These results are obtained only with the use ofborosilicate glass, and not available with lead glass or high silicateglass.

The borosilicate glass used herein may preferably contain about 65 toabout 90% by weight of silicon oxide, typically SiO₂ and about 8 toabout 30% by weight of boron oxide, typically B₂ O₃. Preferredborosilicate glass contains about 75 to about 90% by weight, mostpreferably about 80 to about 84% by weight of silicon oxide and about 8to about 20% by weight, most preferably about 14 to about 18% by weightof boron oxide. Borosilicate glass compositions containing an excessamount of silicon oxide and a less amount of boron oxide have a too lowcoefficient of linear expansion and poor sinterability, resulting in asintered body with a low density. Conversely, Borosilicate glasscompositions containing a less amount of silicon oxide and an excessamount of boron oxide have a too high coefficient of linear expansion.There is a risk of bubbling upon firing so that the sintered body mayhave a low density and have changed its size from the original. It alsohas a high resistivity and a low Q value. The borosilicate glass havingthe above-mentioned composition has another advantage that it littleaffects the internal conductor.

The borosilicate glass may contain up to 5% by weight of aluminum oxide,typically Al₂ O₃, up to 5% by weight of at least one oxide of amonovalent metal M(I) such as K, Na and Li, typically M(I)₂ O, and up to5% by weight of at least one oxide of a divalent metal M(II) such as Ba,Ca, Sr, and Zr, typically M(II)O.

In the other embodiment, the sintered ferrite body further containsboron oxide. More particularly, the sintered ferrite body contains up toabout 10% by weight, more preferably about 0.1 to about 10% by weight,most preferably about 0.5 to about 10% by weight of boron oxide. Theaddition of boron oxide improves the sinterability and mechanicalstrength of the composition. Compositions containing more than about 10%by weight of boron oxide are less resistant to moisture, and thus lessdurable during storage. .It is to be noted that boron oxide is presentin borosilicate glass separate from ferrite grains in the calcinationstep.

The sintered ferrite body of the present invention is generally preparedby any conventional known processes. More particularly, a sinteredferrite body comprising Ni-Cu-Zn ferrite, for example, is prepared bywet blending a predetermined amount of ferrite-forming powder such as amixture of NiO, CuO, ZnO and Fe₂ O₃, and a predetermined amount ofborosilicate glass powder in a ball mill. The powders used have aparticle size of about 0.1 to about 10 μm. The wet mixture is driedusually by a spray dryer, and then calcined. The product is wet groundin a ball mill to a particle size of about 0.01 to about 0.5 μm, driedby a spray dryer, and fired by any of well-known methods.

In the other embodiment, boron oxide powder is added to thelast-obtained ferrite/borosilicate glass mixture, along with a binderand a solvent if desired, before the resulting mixture is fired by anyof well-known methods. The boron oxide powder used herein may have aparticle size of about 0.1 to about 10 μm.

It is also possible to form a paste from necessary powders before it issintered. A sintered body may be obtained by adding a binder such asethyl cellulose and a solvent such as terpineol and butyl carbitol(diethylene glycol mono-n-buthyl ether) to a ferrite/borosilicatemixture and optionally, boron oxide powder to form a paste. The paste isformed into a suitable shape or applied as a sheet by a printing orgreen sheet technique, and sintered at a temperature of up to 950° C.,for example, between 850° C. and 930° C. for about 1/2 to about 4 hours.

Conventional ferrite compositions which are free of borosilicate glassor boron oxide must be sintered at a temperature of about 1,100° C.before a sufficient density can be accomplished. In contrast, acomposition comprising ferrite in admixture with 30% by weight ofborosilicate glass according to the present invention may be fired at alower temperature of 950° C. to an equivalent relative sintered density.

A composition of ferrite and borosilicate glass further containing up to10% by weight of boron oxide according to the present invention may befired at a further lower temperature of 850° to 950° C. to a higherdensity with an additional advantage of a higher deflective strength.

In the above embodiment, a mixture of spinel ferrite and glass isobtained by adding boron oxide powder to a mixture of ferrite-formingpowders and borosilicate glass powder, forming a paste from the mixture,and firing the paste. Ferrite-forming powders, borosilicate glasspowder, and boron oxide powder may be mixed at the same time to form apaste therefrom.

The sintered ferrite body resulting from sintering at lower temperatureshas improved electromagnetic properties, especially their frequencyresponse and improved mechanical strength so that it may be used ascores of various electronic parts, magnetic insulators for chipinductors, magnetic or electromagnetic shields, attenuators, or thelike. The sintered ferrite body may be readily machined. In theapplication as shields, the sintered ferrite body may be used as such orthe body may be finely divided and mixed with a binder before ashielding part is molded therefrom.

FIG. 1 shows one example of a chip inductor according to the presentinvention. The chip inductor designated at 1 has a conventionalwell-known structure as shown in FIG. 1. This inductor may be preparedby a conventional method as by placing internal conductor layers 2 andferrite magnetic layers 3 one on the other to form a ferrite magneticlaminate having an internal conductor of a predetermined pattern such asa spiral pattern and predetermined turns embedded therein, andconnecting opposite ends of the internal conductor 2 to externalelectrodes 41 and 45.

The paste for forming the ferrite magnetic layers 3 of the chip inductor1 may be prepared by the same method as used for the paste for formingsintered ferrite bodies. The internal conductor-forming paste is wellknown and include Ag and Ag-Pd pastes, for example.

A chip inductor may be prepared by alternately applying the ferritemagnetic layer-forming paste and the internal conductor-forming pasteonto a substrate of polyethylene terephthalate, for example, by aprinting or green sheet technique so as to define a predeterminedpattern and firing at a temperature of up to about 950° C., preferablyfrom 850° C. to about 930° C. for about 1/2 to about 4 hours.

The chip inductor thus prepared has high mechanical strength because theferrite magnetic layers contain borosilicate glass and optionally, boronoxide so that they are sintered to a better extent. The sinteringtemperature necessary to obtain a sintered product with an equal densitymay be lower than in the prior art. The chip inductor of the presentinvention also has improved high-frequency response of electromagneticproperties.

The number of ferrite magnetic layers laminated may be chosen dependingon the intended application although one to twenty layers are generallyused. The thickness of each ferrite magnetic layer may be chosendepending on the intended application although the layer is generallyabout 10 to about 30 μm thick. The internal conductor 2 is generallyformed from a metal such as Ag and Ag-Pd and has a thickness of about 10to about 25 μm. The external electrodes 41, 45 may be similarly formedfrom a metal such as Ag and Ag-Pd and has a thickness of about 10 toabout 300 μm.

FIG. 2 shows one example of a composite LC part according to the presentinvention. The composite LC part designated at 5 has an inductor section6 and a capacitor section 7 integrated to each other.

The inductor section 6 is prepared by overlying ferrite magnetic layers61 one on another while interposing internal conductor layers 65 of apredetermined pattern therebetween so as to keep conduction betweenconsecutive conductor segments. The capacitor section 7 which isintegrated to the inductor section 6 is prepared by alternately placinginternal electrode layers 75 and ceramic dielectric layers 71.

In the example shown in FIG. 2, the inductor and capacitor sections 6and 7 have a plurality of inductance (L) and capacitance (C),respectively. External electrodes 8 are connected so as to form adesired LC circuit with the inductor and capacitor sections.

The inductor section 6 of the composite LC part 5 has substantially thesame structure as the chip inductor shown in FIG. 1. The inductorsection can be obtained by sintering at a lower temperature, hasimproved frequency response and mechanical strength. The percentshrinkage of the ferrite magnetic layer may be controlled by adding aproper amount of borosilicate glass to ferrite so that the shrinkage ofthe inductor section 6 may be approximately equal to the shrinkage ofthe capacitor section 7. Then any warpage or separation is avoided atthe interface between the inductor and capacitor sections duringsintering.

More particularly, nickel base ferrite generally has a coefficient oflinear expansion of 90×10⁻⁷ to 115×10⁻⁷ /deg. A composition of nickelbase ferrite having 17 to 75% by weight of borosilicate glass addedthereto has a coefficient of linear expansion reduced to 70×10⁻⁷ to90×10⁻⁷ /deg. The latter value is approximately equal the coefficient oflinear expansion of 75×10⁻⁷ to 85×10⁻⁷ /deg. of titanium dioxide basedielectric material used in the dielectric layers of the capacitorsection. The composition of nickel base ferrite and borosilicate glasshas a shrinkage of about 15 to about 20%, which is approximately equalto the shrinkage of about 15 to about 18% of titanium dioxide basedielectric material.

As mentioned above, according to the present invention, a coefficiientof linear expansion and a shrinkage can be controlled to the desiredvalue by adding the borosilicate glass.

When the ferrite magnetic layers of the inductor section 6 contain up to10% by weight of boron oxide, the inductor section has a higher densityat the end of sintering. Thus, the composite LC part has highermechanical strength.

The material of which the dielectric layers 71 of the capacitor section7 are made may be any desired dielectric material, but preferablytitanium dioxide base dielectric material. The titanium dioxide basedielectric material used herein contains a major proportion of TiO₂ andmay contain up to 10 mol % in total of NiO, CuO, Mn₃ O₄, Al₂ O₃, MgO orSiO₂ or a mixture thereof when a dielectric loss and a coefficient oflinear expansion are taken into account. Titanium dioxide basedielectric material has a shrinkage of about 15 to about 18%. Theferrite composition having borosilicate glass added thereto has asimilar shrinkage as described above.

The number of dielectric layers in the capacitor section 7 may be chosendepending on the intended application although one to ten layers aregenerally used. The thickness of each dielectric layer is generallyabout 50 to about 150 μm thick. The internal electrode in the capacitorsection is generally formed from a metal such as Ag and Ag-Pd and has athickness of about 5 to about 15 μm.

The number of ferrite magnetic layers laminated in the inductor section6 may be chosen depending on the intended application although one totwenty layers are generally used. The thickness of each ferrite magneticlayer may be chosen depending on the intended application although thelayer is generally about 10 to about 30 μm thick. The internal conductoris generally formed from a metal such as Ag and Ag-Pd and has athickness of about 10 to about 30 μm.

The external electrode is generally formed from a metal such as Ag andAg-Pd and has a thickness of about 10 to about 300 μm.

The composite LC part of the present invention may be prepared by any ofconventional well-known printing and green sheet techniques. Moreparticularly, pastes for ceramic magnetic layers, dielectric layers,internal electrodes and conductors are prepared and applied one by oneonto a substrate of polyethylene terephthalate by a printing or greensheet technique.

Those pastes for forming dielectric layers and internal electrode layersof the capacitor section, internal conductor layers of the inductorsection, and external electrodes may be prepared using suitable binderand solvent. The capacitor and inductor sections are prepared byapplying the necessary pastes onto a substrate in laminate form by aprinting or green sheet technique. The laminate is cut to apredetermined shape, separated from the substrate, and fired at atemperature of up to 950° C., for example 850° to 930° C. The firingtime is from about 1/2 to about 4 hours. At the end of firing, silverpaste is baked to the laminate to form external electrodes.

The dimensions of the composite LC part thus prepared may be chosendepending on the intended application.

The sintered ferrite body of the present invention contains borosilicateglass in admixture with ferrite. A composition of ferrite andborosilicate glass can be fired even at a lower temperature of up to950° C. into a sintered body having a high density and mechanicalstrength. The sintered body has improved machinability andelectromagnetic properties in a high frequency band.

The chip inductor uses the sintered ferrite body as its magnetic layerso that it can be fired at a relatively low temperature into a producthaving high mechanical strength and improved electromagnetic propertiesin a high frequency band.

The composite LC part uses the chip inductor as its inductor section sothat it can be fired at a relatively low temperature into a producthaving high mechanical strength and improved electromagnetic propertiesin a high frequency band. The percent shrinkage of the inductor sectionmay be equalized to that of the capacitor section by adding a controlledamount of borosilicate glass to ferrite. Then occurrence of warpage orseparation at the interface of the inductor and capacitor sections dueto the difference therebetween of shrinkage upon sintering can beavoided. Difficulty of surface packaging due to warpage or separation isleft no longer.

EXAMPLES

In order that those skilled in the art will better understand thepractice of the present invention, examples of the present invention aregiven below by way of illustration and not by way of limitation.

EXAMPLE 1

A sintered ferrite body was prepared by formulating a paste therefor byblending nickel base ferrite-forming powder with borosilicate glass andoptionally, boron oxide B₂ O₃. The Ni base ferrite-forming powder usedwas a powder mixture of NiO and Fe₂ O₃ having a particle size of about0.1 to 1.0 μm. The mixture consisted of 52 mol % of nickel powdercalculated as NiO and 48 mol % of iron powder calculated as Fe₂ O₃. Theborosilicate glass used was a borosilicate glass powder, designatedGlass I, consisting of 80.3% by weight of SiO₂, 17.5% by weight of B₂O₃, and 2.2% by weight of K₂ O and having a particle size of 5 μm. Theblend of Ni base ferrite-forming powder and borosilicate glass powderwas wet milled in a ball mill.

The wet mixture was dried by a spray dryer, calcined into granules at850° C., again ground in a ball mill, dried by a spray dryer intoparticles having an average particle size of 0.1 μm.

The resulting powder alone or in admixture with boron oxide (B₂ O₃)powder having an average particle size of 5.0 μm was dispersed interpineol along with a predetermined amount of ethyl cellulose, andmixed in a Henschel mixer to obtain a paste from which a sinteredferrite body is to be formed.

The paste was applied on a polyethylene terephthalate substrate by aprinting technique. The laminate was separated from the substrate andfired at 900° C. for 2 hours, obtaining a bar-shaped sample of3.0×3.0×15.00 mm.

The sample was measured for relative sintered density (sintereddensity/theoretical density), coefficient of linear expansion, andshrinkage, which are reported in Table 1. Sample No. 1 is a sampleobtained from the nickel base ferrite-forming powder without blendingglass ingredient.

Table 1 also shows the results of other samples using the followingglass compositions.

Glass II: high silicate glass

95% by weight of SiO₂

5% by weight of Na₂ O

Glass III: lead glass

42% by weight of SiO₂

52% by weight of PbO

5.5% by weight of Al₂ O₃

0.5% by weight of B₂ O₃

Glass IV: borosilicate glass

70% by weight of SiO₂

25% by weight of B₂ O₃

5% by weight of Na₂ O

Glasses II and III are outside the scope of the present invention.Sample No. 10 is a prior art ferrite composition consisting of 45.5 mol% of Fe₂ O₃, 44 mol % of NiO, 8 mol % of CuO, 2 mol % of ZnO, and 0.6mol % of CoO.

                  TABLE 1                                                         ______________________________________                                                        Glass          Relative                                       Sample          Content  B.sub.2 O.sub.3                                                                     sintered                                                                              Shrinkage                              No.    Type     (wt %)   (wt %)                                                                              density (%)                                                                           (%)                                    ______________________________________                                         1*    --       --       --    92      16.0                                   2      Glass I  28       --    97      16.5                                   3      Glass I  42       --    97.5    19.5                                   4      Glass I  28       2     98      20.0                                   5      Glass I  28       8     98.5    21.5                                   6      Glass I  28       15    98.8    22.2                                    7*    Glass II 30       --    72      1.6                                     8*    Glass III                                                                              30       --    95      16.0                                   9      Glass IV 30       --    96      23.2                                   10*    --       --       --    75      6.3                                    ______________________________________                                         *comparison                                                              

As seen from Table 1, sample Nos. 2 to 6 and 9 falling within the scopeof the present invention could be fired at a relatively low temperatureinto a sintered body having a high density and mechanical strength.Their shrinkage was as high as 16.5 to 23.2%.

These shrinkage values are approximately equal to the shrinkage of TiO₂base dielectric material which ranges from 15 to 18%. This indicatesthat when the ferrite composition of the present invention is used toform an inductor section, there will be obtained a composite LC partwhich is free of warpage, separation or crack. This will be laterdemonstrated in Example 3.

Sample Nos. 2 and 10 were fired at different temperatures ranging from800° C. to 950° C. and measured for relative sintered density. Theresults are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Relative Sintered Density                                                     Sintering                                                                     temperature   Sample No. 2                                                                             Sample No. 10                                        ______________________________________                                        800° C.                                                                              90%        65%                                                  850° C.                                                                              95%        68%                                                  900° C.                                                                              97%        75%                                                  950° C.                                                                              98%        86%                                                  ______________________________________                                    

Cores were formed from the composition of sample Nos. 2 and 8 andmeasured for a magnetic loss at varying frequency. The magnetic loss ofsample No. 8 was at least twice larger than that of sample No. 2 atfrequencies of 500 MHz or higher.

EXAMPLE 2

A chip inductor of 3.2 mm×2.5 mm×1.0 mm as shown in FIG. 1 was preparedby alternately applying the ferrite paste of sample No. 2, 4, 7, 8, 9 or10 and silver paste by a laminate printing technique to form analternate laminate of magnetic layers and internal conductor layers.Each ferrite layer was 40 μm thick. Each conductor layer had a thicknessof 20 μm and a width of 300 μm. The conductor layers formed 21/2 turnsof elliptical coil having a major diameter of 2.5 mm and a minordiameter of 1.3 mm. External electrodes were formed from Ag-Pd paste.Sintering was carried out at a temperature of 870° C. for 2 hours.

The thus obtained chip inductors were measured for Q value andinductance (L) at varying frequency. The results are shown in Table 3.

For comparison purposes, a coreless coil was prepared using as themagnetic layer a non-magnetic material consisting essentially of 46 mol% of Fe₂ O₃, 44 mol % of ZnO and 10 mol % of CuO and having 1 atom % ofeach of CoO and MnO added. The results of the coreless coil are alsoshown in Table 3.

                  TABLE 3                                                         ______________________________________                                        Sample               Frequency (MHz)                                          No.    Glass         50     100  200   300  500                               ______________________________________                                        2      Glass I  L (nH)   25   30   40    40   40                                              Q        21   28   35    29   20                              4      Glass I  L (nH)   26   32   42    41   41                                              Q        22   29   37    30   22                               7*    Glass II L (nH)   10   11   11    15   15                                              Q        15   20   20    22   18                               8*    Glass III                                                                              L (nH)   --   --   --    --   --                                              Q        --   --   --    --   --                              9      Glass IV L (nH)   24   26   31    30   30                                              Q        20   25   27    25   20                              10*    --       L (nH)   105  125  410   --   --                                              Q        37   37    3    --   --                              Coreless                                                                             --       L (nH)   10   10   15    20   20                              coil            Q        16   21   21    25   17                              ______________________________________                                    

As seen from Table 3, the samples of the present invention have superiorfrequency response of inductance and Q value to the comparative samples.Sample No. 7 containing Glass II, high silicate glass in the magneticlayers had lower strength than the remaining samples. Sample No. 8containing Glass III, lead glass in the magnetic layers was unmeasurablebecause lead caused silver in the internal conductor layers to diffuseso that the electrode locally disappeared or was disconnected.

Similar experiments were carried out by replacing the ferrite-formingpowder by other various Ni-Zn ferrite-forming powders and replacing theglass material by 30% by weight of other various borosilicate glasses.Similar results were obtained.

Also, similar results were obtained in similar experiments which werecarried out with compositions containing Ni-Cu ferrite and 25% by weightof borosilicate glass, Ni-Cu-Zn ferrite and 28% by weight ofborosilicate glass, and Ni-Cu-Zn-Li ferrite and 23% by weight ofborosilicate glass, % by weight being based on the total weight of eachcomposition.

EXAMPLE 3

A composite LC part comprising inductor and capacitor sections wasprepared.

A magnetic layer-forming paste was prepared by adding borosilicate glassto Ni base ferrite-forming powder such that the content of borosilicateglass ranged from 10 to 80% by weight of the mixture. The Ni baseferrite-forming powder used was a powder mixture of NiO, CoO and Fe₂ O₃having a particle size of about 0.1 to 1.0 μm. The mixture consisted of52 mol % of nickel powder calculated as NiO and 48 mol % of iron powdercalculated as Fe₂ O₃, and contained 0.4% by weight of CoO. Theborosilicate glass used was a borosilicate glass powder consisting of82.0% by weight of SiO₂, 16.0% by weight of B₂ O₃, 0.3% by weight of Al₂O₃, and 1.7% by weight of K₂ O and having an average particle size of 5μm. The blend of Ni base ferrite-forming powder and borosilicate glasspowder was wet milled in a ball mill.

The wet mixture was dried by a spray dryer, calcined into granules at800° C., again ground in a ball mill, dried by a spray dryer intoparticles having an average particle size of 0.1 μm.

The resulting powder was dispersed in terpineol along with apredetermined amount of ethyl cellulose, and mixed in a Henschel mixerto obtain a paste from which a ceramic magnetic layer is to be formedfor the inductor section.

The paste was applied onto a polyethylene terephthalate substrate by aprinting technique. The laminate was separated from the substrate andfired at 870° C. for 2 hours, obtaining a bar-shaped sample of3.0×3.0×15.00 mm.

The sample was measured for coefficient of linear expansion, which isreported in Table 4. Table 4 also shows the results of other samplesusing Glasses II, III and IV whose composition is identified in Example1.

                  TABLE 4                                                         ______________________________________                                                                 Coefficient of linear                                Glass        Content (wt %)                                                                            expansion (x10.sup.7 /deg)                           ______________________________________                                        none (NiFe.sub.2 O.sub.4)                                                                   0          115                                                  Borosilicate glass                                                                         10          104                                                  Borosilicate glass                                                                         20          96                                                   Borosilicate glass                                                                         30          82                                                   Borosilicate glass                                                                         40          74                                                   Borosilicate glass                                                                         50          65                                                   Borosilicate glass                                                                         60          62                                                   Borosilicate glass                                                                         70          48                                                   Borosilicate glass                                                                         80          43                                                   Glass II     25          92                                                   Glass III    40          88                                                   Glass IV     50          96                                                   SiO.sub.2    20          85                                                   TiO.sub.2 base dielectric                                                                  --          85                                                   ______________________________________                                    

The shrinkage of these samples was measured, with the results shown inTable 5.

                  TABLE 5                                                         ______________________________________                                        Glass          Content (wt %)                                                                            Shrinkaqe (%)                                      ______________________________________                                        none (NiFe.sub.2 O.sub.4)                                                                     0          16.5                                               Borosilicate glass                                                                           30          14.5                                               Glass II       25          8.0                                                Glass III      40          17.1                                               Glass IV       50          20.3                                               SiO.sub.2      20          0.5                                                TiO.sub.2 base dielectric                                                                    --          16.7                                               ______________________________________                                    

It is to be noted that the bottom line in Tables 4 and 5 showscorresponding values of TiO₂ base dielectric material of which adielectric layer is formed to constitute the capacitor section.

As seen from Tables 4 and 5, the ferrite compositions containingborosilicate glass according to the present invention can have acoefficient of linear expansion and a shrinkage approximately equal tothose of the TiO₂ base dielectric layer.

Table 6 shows the initial magnetic permeability (μi) of some samples at100 MHz.

                  TABLE 6                                                         ______________________________________                                        Glass           Content (wt %)                                                                            μi                                             ______________________________________                                        none (NiFe.sub.2 O.sub.4)                                                                      0          13.1                                              Borosilicate glass                                                                            30          2.5                                               ______________________________________                                    

As seen from Table 6, the ferrite/borosilicate glass compositionaccording to the present invention has a reduced initial magneticpermeability, indicating that the frequency response of the magneticlayer on a high frequency side is improved.

Next, another paste from which a dielectric layer is to be formed forthe capacitor section was prepared from a powder having a compositionconsisting of 91% by weight of TiO₂, 3% by weight of NiO, 3% by weightof CuO, and 3% by weight of Mn₃ O₄ and an average particle size of 0.1to 1.0 μm, using the same binder and solvent as used in the magneticlayer-forming paste.

The magnetic layer-forming paste containing 30% by weight ofborosilicate glass (based on the total of ferrite and borosilicateglass), the dielectric layer-forming paste, and Ag paste for forminginternal electrode and conductor were applied by a printing technique toform a laminate. The inductor section included 10 magnetic layers eachhaving a thickness of 40 μm. The capacitor section included 2 dielectriclayers each having a thickness of 100 μm. The internal electrode andconductor each were 20 μm thick.

The laminate was sintered at 870° C. for 2 hours. The laminate wasgradually cooled, obtaining a composite LC part of 4.5 mm×3.2 mm×1.5 mmconstituting a high-pass filter circuit for 100 MHz and higher bandpass.

In the composite LC part, no warpage, separation or cracking wasobserved at the interface between the capacitor and inductor sections.The internal conductor experienced no deterioration of its properties. Acomparative part having a magnetic layer of borosilicate glass-freeferrite in the inductor section had a passband of 100-500 MHz whereasthe present part had the upper limit of its passband extended towardhigher frequencies by 500 MHz and had a passband of 100 MHz to 1 GHz.

In those samples using Glass II, Glass IV, and SiO₂, warpage, separationor cracking occurred. In the sample using Glass III, the internalconductor deteriorated its properties.

A specimen was observed under a microscope for warpage, separation orcracking. For each sample, 100 specimens were tested. The number ofdeficient specimens per 100 specimens is reported in Table 7.

A specimen was kept at a temperature of 40° C. and a relative humidityof 85-90% for 1,000 hours before the resistance of its internalconductor was measured. For each sample, 100 specimens were tested. Thenumber of those specimens whose resistance changed more than 10% fromtheir initial resistance is reported in Table 7.

                  TABLE 7                                                         ______________________________________                                                    Content  Deficient Resistance changed                             Glass       (wt %)   specimens*                                                                              specimens*                                     ______________________________________                                        none (NiFe.sub.2 O.sub.4)                                                                  0       87        0                                              Borosilicate glass                                                                        30        0        0                                              Glass II    25       56        5                                              Glass III   42       98        86                                             Glass IV    60       62        36                                             SiO.sub.2   20       100       --                                             ______________________________________                                         *per 100 specimens                                                       

EXAMPLE 4

A powder mixture of ferrite-forming powder and borosilicate glass powderhaving the same composition as in Example 3 was prepared by the sameprocedure as in Example 3.

The resulting powder and boron oxide (B₂ O₃) powder having an averageparticle size of 5.0 μm were dispersed in terpineol along with apredetermined amount of ethyl cellulose, and mixed in a Henschel mixerto obtain a paste from which a ceramic magnetic layer is to be formedfor the inductor section.

The paste was applied onto a polyethylene terephthalate substrate by aprinting technique. The laminate was separated from the substrate andfired at 870° C. for 2 hours, obtaining a bar-shaped sample of3.0×3.0×15.00 mm.

The sample was measured for coefficient of linear expansion andshrinkage, which are reported in Tables 8 and 9. There are also shownthe results of other samples using Glasses II, III and IV whosecomposition is identified in Example 1.

                  TABLE 8                                                         ______________________________________                                                     Glass   B.sub.2 O.sub.3                                                       content Content  Coefficient of linear                           Glass        (wt %)  (wt %)   expansion (x10.sup.-7 /deg)                     ______________________________________                                        none (NiFe.sub.2 O.sub.4)                                                                   0      --       115                                             Borosilicate glass                                                                         10      2        105                                             Borosilicate glass                                                                         20      2        95                                              Borosilicate glass                                                                         30      2        85                                              Borosilicate glass                                                                         40      2        75                                              Borosilicate glass                                                                         50      2        67                                              Borosilicate glass                                                                         60      2        63                                              Borosilicate glass                                                                         70      2        50                                              Borosilicate glass                                                                         80      2        45                                              Glass II     25      --       92                                              Glass III    40      --       88                                              Glass IV     50      --       96                                              SiO.sub.2    20      --       85                                              TiO.sub.2 base dielectric                                                                   0      --       85                                              ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                                    Glass       B.sub.2 O.sub.3                                                                           Shrink-                                   Glass       Content (wt %)                                                                            Content (wt %)                                                                            age (%)                                   ______________________________________                                        none (NiFe.sub.2 O.sub.4)                                                                  0          --          16.5                                      Borosilicate glass                                                                        30          2           16.8                                      Glass II    25          --          8.0                                       Glass III   40          --          17.1                                      Glass IV    50          --          20.3                                      SiO.sub.2   20          --          0.5                                       TiO.sub.2 base dielectric                                                                  0          --          16.7                                      ______________________________________                                    

It is to be noted that the bottom line in Tables 8 and 9 showscorresponding values of TiO₂ base dielectric material of which adielectric layer is formed to constitute the capacitor section.

As seen from Tables 8 and 9, the ferrite compositions containingborosilicate glass according to the present invention can have acoefficient of linear expansion and a shrinkage approximately equal tothose of the TiO₂ base dielectric layer.

Samples having the same composition as above were prepared while theamount of boron oxide B₂ O₃ added was varied as shown in Table 10. Thesesamples were measured for deflective strength. The amounts ofborosilicate glass and boron oxide added are expressed in % by weightbased on the total weight of the composition of ferrite, borosilicateglass and boron oxide.

                  TABLE 10                                                        ______________________________________                                        Borosilicate  B.sub.2 O.sub.3                                                                       Deflective                                              glass (wt %)  (wt %)  strength (kgf/mm.sup.2)                                 ______________________________________                                         0            0       8.7                                                     30            0       3.5                                                     30            0.5     6.1                                                     30            1       7.5                                                     30            1.5     8.9                                                     30            2       10.0                                                    30            3       10.3                                                    30            4       10.0                                                    30            6       9.7                                                     30            8       8.5                                                     30            10      8.0                                                     30            15      7.5                                                     ______________________________________                                    

As seen from Table 10, the addition of boron oxide is effective inincreasing mechanical strength. The sintered ferrite compositioncontaining 15% by weight of boron oxide was less resistant to moisture.

Table 11 shows the initial magnetic permeability (μi) of some samples at100 MHz.

                  TABLE 11                                                        ______________________________________                                        Borosilicate      B.sub.2 O.sub.3                                             glass (wt %)      (wt %)  μi                                               ______________________________________                                         0                0       13.1                                                30                2       2.5                                                 ______________________________________                                    

As seen from Table 11, the ferrite/borosilicate glass/boron oxidecomposition according to the present invention has a reduced initialmagnetic permeability, indicating that the frequency response of themagnetic layer on a high frequency side is improved.

A composite LC part was prepared by the same procedure as in Example 3.No warpage, separation or cracking was observed at the interface betweenthe capacitor and inductor sections of the composite LC part. Theinternal conductor experienced no deterioration of its properties. Thepresent part had the upper limit of its passband extended toward higherfrequencies by about 500 MHz as compared with a part having a magneticlayer of borosilicate glass-free ferrite.

In those samples using Glass II, Glass IV, and SiO₂, warpage, separationor cracking occurred. In the sample using Glass III, the internalconductor deteriorated its properties.

A specimen was observed under a microscope for warpage, separation orcracking. For each sample, 100 specimens were tested. The number ofdeficient specimens per 100 specimens is reported in Table 12.

A specimen was kept at a temperature of 40° C. and a relative humidityof 85-90% for 1,000 hours before the resistance of its internalconductor was measured. For each sample, 100 specimens were tested. Thenumber of those specimens whose resistance changed more than 10% fromtheir initial resistance is reported in Table 12.

                  TABLE 12                                                        ______________________________________                                                    Glass                    Resistance                                           Content  B.sub.2 O.sub.3                                                                       Deficient                                                                             changed                                  Type        (wt %)   (wt %)  specimens*                                                                            specimens*                               ______________________________________                                        none         0       0       87      0                                        Borosilicate glass                                                                        30       0        0      0                                        Borosilicate glass                                                                        30       2        0      0                                        Borosilicate glass                                                                        30       4        0      0                                        Borosilicate glass                                                                        30       15       0      2                                        Glass II    25       --      56      5                                        Glass III   42       --      98      86                                       Glass IV    60       --      62      36                                       SiO.sub.2   20       --      100     --                                       ______________________________________                                         *per 100 specimens                                                       

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

We claim:
 1. A sintered ferrite body, consisting essentially of:a nickelbased ferrite in combination with from about 15 to about 75% by weightof the body of a borosilicate glass, said borosilicate glass containingabout 75 to about 90% by weight of silicon oxide, about 8 to about 20%by weight of boron oxide, 0 to about 5% by weight aluminum oxide, 0 toabout 5% by weight of at least 1 oxide of a monovalent metal and 0 toabout 5% by weight of at least 1 oxide of a divalent metal, saidpercentages based on the weight of borosilicate glass.
 2. The sinteredferrite body of claim 1, wherein said nickel based ferrite is aNi-ferrite, a Ni-Cu ferrite, a Ni-Zn ferrite, or a Ni-Cu-Zn ferrite. 3.The sintered ferrite body of claim 1, wherein the nickel content of saidferrite ranges from about 45 to about 55 mol % of the ferrite calculatedas NiO.
 4. The sintered ferrite body of claim 3, wherein a portion ofsaid nickel is replaced by up to 40 mol % of Cu, Zn or Li.
 5. Thesintered ferrite body of claim 1, wherein the content of theborosilicate glass in the ferrite-borosilicate glass combination rangesfrom about 25 to 35% by weight.
 6. A sintered ferrite body, consistingessentially of:a combination of a nickel based ferrite, up to about 10%by weight of boron oxide, based on the weight of the body, and fromabout 15 to about 75% by weight, based on the weight of the body, of aborosilicate glass, said borosilicate glass containing about 75 to 90%by weight of silicon oxide, about 8 to about 20% by weight of boronoxide, 0 to about 5% by weight of aluminum oxide, 0 to about 5% byweight of at least one oxide of a monovalent metal and 0 to about 5% byweight of at least one oxide of a divalent metal, said percentages basedon the weight of borosilicate glass.
 7. The sintered ferrite body ofclaim 6, wherein the boron oxide powder combined with nickel basedferrite and borosilicate glass has a particle size range of about 0.1 toabout 10 μm.